Rectifier tube



S P 7, 5 L. MALTER RECTIFIER TUBE Filed Sept. 30, 1952 Patented Sept. 7,1954 UNITED S TATES PATENT O FF I CE RECTIFIER Louis Malter, Princeton,N. J iassignor .to .Radio -Corporation of America, a corporationvo'f'Dela- "ware Applicationseptembcr 30,319.52, :Serial No. 312,348

10'Claims.

1 .Thisinventionrelate to gaseous dischargedevices .and particularly to.gaseous discharge devices thatare used for purposes .of rectification.If .a vacuum type of dischargedevi'ce, ortube,

.is used .for purposes of .rectificationla large applied potential isrequired to overcome the-space charge efiect when the tube isconducting. As

-is wellknown, the space charge eifectmaybe essentially eliminated byinserting a. gaseous filling in the tube. The gaseous filling willionizewhen the tube conducts and will thus 'form a highly conductive plasmawithin the tube. The plasma .is a region of very high, but essentiallyequal,

concentrations .ofiree electrons andpositive ions.

Due to .the'high mobility o'fthep-lasma electrons and the absence of netspace charge, the plasma is an excellent electrical conductor. Thus thegaseous discharge type of .device has the advantageofeliminatingthespace charge eifects'when related to a .vacuum type ofdischarge device.

Even though thegaseous type ofdischarge device has considerableadvantage over a'vacuum' type .ference in potential between the cathodeand anode during the conductive period for *a given load current, and isrequired 'to maintain the plasma 'in-the tube. One of the reasonsfithatthe arc drop occurs is that the plasma will .li'fiuseoif 'tovariouselectrodes and insulating members and -will thus require additionali'ree electrons and positive ':ions to be generated to replace thosethat are lost. Aifurther reason for the arc drop :is the recombinationof electrons Band positive -1ons.

One methodto .overcomeasome of the troublesome effects of :the .arc dropis to separate the ionizing discharge from the work or load :currentpath through the tube. uVh'en this LiSad'OIlB the a-plasma, may :begenerated 'by :an auxiliary discharge while the load :current .circu'itof the tu'be is-serving its useful purpose more efficiently.

Several methods have been devised to=separate thesetwo functions, ire.C1 thei'unction of providing electronswith sufficient energy to generate0 ions for sustaining the plasma, and (2) the function of providing"theelectrici'ield neededfor-pull- 'ing a given anode current throughthe'tube, "and thus achieve a more efficient "gaseous rectifying tube.The reasonthat a more "efficient gas tube is developed whenlthe twofunctionsare separated is that the potential neededfor-drawinganelectron .current is small (as compared to *.the;potenti-al required .to maintain the discharge, thus :the mosteflicient voltage magnitude may be utilized when :the iunctions areseparated. All of these .methods that have been devised :for separatingthese functions have required a direct current potential to provide theelectrodes with sufficient energy to produce a sustained ionization. The'fact that.a direct -current has been required to sustain the .plasmahas many disadvantages. One of .the principal disadvantages is that whenthe device is -.to be .used for rectification .purposes asdirect currentsource must be .available.

It is therefore .an object vof .this invention to provide anew and novelgas discharge device that will overcome the requirementlof adirect-current source and willpermit the separationof the abovementionedfunctions.

It is a further-object of this invention 'to provide a new and novelgaseous discharge device that maybe used for purposes of rectificationWiherein all of the electrodes are energized with an alternating currentsource.

"It 'isa still further object of this invention .to provide .a new andnoveltgaseous dischargedevice that 'will separate the functions ofsustaininga conductive plasma and drawing -a load current "with all oftheelectrodes'ibeing energized with an "alternating current source.

.It is astillfurther object of this invention .to "provide a knew and:novel "rectifying device of the gaseous idischarge type wherein theplasma is 'm'ainta'inedbyalternating current.

It is :a still further object of this invention to provide a novelapparatus including a gas discharge device and circuit "therefor wherein"the elements of "the discharge device .are energized Withan alternatingcurrent source to produce a sustained plasma throughout the device.

Tn accordance "with the general aspects 'of this invention thereisprovided a-neWan'd-novel gaseous discharge "device embodying 'aconstruction wherein'allpffthe electrodes are energized "by analternating current source and wherein'the'function of ionizing thegaseou filling is separated from the load currentpath through the.device. 133? means of this separation of functions within thedevi'ce'that is operated with an alternating current-"the arc drop alongthe load current path is greatly reduced while a sustained ionization isgenerated "by means of an alternating current. 'One specific embodiment"of this "invention "is 'a pair of "auxiliary cathodes that willdischarge between each other during both the forward and inverse halfcycles.

These and other features and advantages will best be understood from thefollowing description of the illustrated embodiments when read inconnection with the accompanying drawings wherein similar referencecharacters designate similar parts throughout the several views and inwhich:

Figure 1 is a sectional view of a gaseous discharge device, which may beused for the purpose of half wave rectification, made in accordance withthis invention;

Figure 2 is a transverse sectional view of Figure 1 taken along line 2-2of Figure 1;

Figure 3 is a cross sectional view of a gaseous discharge device made inaccordance with this invention that is adapted for full waverectification;

Figure 4 is an example of a circuit diagram for the one-half waverectifying device shown in Figures 1 and 2;

Figure 5 is an example of a circuit diagram for the full-wave rectifyingdevice shown in Figure 3;

Figure 6 is a sectional view of a modification of the gaseous dischargedevice shown in Figures 1 and 2 and is especially adapted for one-halfwave rectification; and

Figure 7 is a circuit diagram which may be used with the device shown inFigure 6.

Referring now to Figures 1 and 2, there is shown a gaseous dischargedevice comprising a sealed envelope 8 containing an ionizable medium G.Any suitable media may be utilized. The pressure for any particularembodiment will be in accordance with its specific electrode geometryand spacings but is not at all critical and may be varied over wideranges. A number of tubes of the type under consideration have beenfound to operate satisfactorily with a filling of helium of a pressureof approximately 750 microns. However, as is well known, other media andother pressures may be used, c. g. pressure which lie in any rangebetween approximately 100 microns and several millimeters of mercury.The envelope 8 has the usual reentrant stem III to support the variouselements.

Inside of the envelope 8 is an anode I2 which is shown as tubular inshape. This specific shape of the structure is not critical, although itdoes offer certain advantages for ion trapping, etc. Surrounded by theanode I2 is a main cathode I4 which may be of the conventional oxidecoated type. Also within the anode I2 are two auxiliary cathodes I 6 andI8 which also may be of the conventional oxide coated type of thermioniccathode. These elements are supported, as is shown more clearly inFigure 2, by end micas 2!] and 2I, which are held in place by end rods22.

In operation of this device a potential difference sufficiently high tocause ionization of the gaseous filling is applied between the auxiliarycathodes I6 and I8. I prefer to apply an alternating current otentialbetween these electrodes so that a battery supply or a similar sourcewill not be required. When this potential is applied, one of thecathodes will act as an anode during one-half of the cycle and then whenthe cycle reverses the other cathode will act as an anode during thebalance of the cycle. By means of using these two cathodes, that areenergized by an alternating current source, the gaseous filling of thetube is continuously ionized for all practical purposes, thus forming acontinuous conductive plasma. Of course there is a period of time, whenthe cycle is changing, when no electrons are provided to produce theionization i. e., when the potential difference between the auxiliarycathodes is less than the ionization potential. However, this slighttime will not be suflicient to permit deionization so that the ionizedgaseous atmosphere i. e., the plasma, will continuously be present.

The plasma, which occupies the space throughout the inside of theenvelope 8, behaves like a low impedance conductor. Furthermore, due tothe essential equality therein of charges of opposite signs no electronspace charge effects are present. Due to the fact that the plasma is alow impedance conductor, there is effectively connected between the maincathode I4 and the anode I2 a low impedance conductor that conductselectrons when the anode I2 is positive with respect to the main cathodeI4.

When the ionization producing discharge function is separated from thework discharge function the potential applied to the work circuitelectrodes may be much smaller than the ionization potential of thegaseous filling and thus it has been found that very small voltages canbe rectified in a very efiicient manner. The potential applied to a workcircuit may exceed the ionization potential provided the dro in a loadresistor is sufficiently great so that the potential across the mainelectrodes does not exceed the ionization potential. This condition canalways be satisfied by making the auxiliary discharge currentsufiiciently large provided that one has not exceeded the emissioncapabilities of the main cathode.

The specific arrangement of the various electrodes is not particularlycritical although this arrangement does offer some definite advantages.With the anode I2 surrounding all of the oathodes, and closed on theends by micas 20 and 2 I, a partial ion trap will be formed which willpermit more efficient operation of the device. Once the plasma is formedit will not tend to diffuse out of the main discharge region to thevarious other structures in the tube. When desired the end insulatingmembers 20 and 2| may be constructed of a conductive material andconnected to the anode I2 which will be a complete ion trap. When thisis done, i. e. the members 20 and 2I are constructed of metal someinsulators are provided for the cathodes to insulate them from the anodeI2.

The particular location of the auxiliary cathodes I6 and I8 with respectto the main cathode I4 is also not particularly critical. The primarypurpose of the auxiliary cathodes I6 and I8 is to provide the conductiveplasma between the main cathode I4 and the anode I2. Any arrangement ofthe auxiliary cathodes that will produce a plasma that is continuous,for all practical purposes, will be acceptable and is contemplated bythis invention.

In Figure 3 there is shown a device that is adapted for full waverectification purposes. In this embodiment of the invention the envelope8 contains a pair of anodes 24 and 25. The pair of anodes 24 and 25enclose the main cathode I4 as well as the pair of auxiliary cathodes I6and I8. The specific cathode structures may be the same as was describedin connection with Figures 1 and 2. The primary purpose is to provide asustained lasma between the main cathode I4 and the main anodes 24 and25.

The main anodes 24 and 25 enclose the cathodes and are supported byinsulating members and 2| and support rods 22 as in Figure 2. Here againthe insulating members 20 and 2| may be constructed of a conductivematerial and thus made a part of the anodes. The main anodes 24 and arespaced apart, as shown in Figure 3, or some type of insulating materialmay be inserted between the two anodes.

Figure 4 is a circuit diagram utilizing this invention for the purposeof half-wave rectification for the device shown in Figure 1. An al--tcrnating current is applied to the auxiliary cathodes I 6 and I8 bymeans of the auxiliary input transformer 32. A current limiting resistor3|] is connected in the circuit as shown. The alternating currentapplied to the auxiliary cathodes l6 and I8 is sufficient to causeionization of the gaseous filling G to thus form the conductive plasma.

The potential that is to be rectified is applied to the main cathode [4by means of the main input transformer 34. Connected between the anodel2 and one side of the secondary of main input transformer 34 is aconventional filter circuit consisting of capacitor 36, inductor 38 andcapacitor 40. Connected to the output of the filter circuit is the loaddesigned as L. Some acceptable values for the filter circuit are 20 mfdfor the capacitors 36 and 40, and 10 henries for the coil 38. Thesevalues are not intended to be controlling but merely representative ofvalues that are acceptable for eificient operation at 60 cycles.

The potential to be rectified may be of any desired magnitude and theonly limitation will be when a glow discharge takes place from the anodeIE to the main cathode l4. The approximate voltage at which the glowdischarge will take place in a device of this type is of the order ofhundreds to thousands of volts depending upon many factors including thetype of gaseous filling, the electrode geometry etc. The reason thatthousands of volts may be rectified by the device is that a much greaterportion of the applied voltage will appear across the load L. Thepotential magnitude limitation being when the voltage across theelectrodes is sufficient to cause an inverse glow discharge. When thepotential between the cathode l4 and the anode I2 exceeds the ionizationpotential the device will continue to function as a rectifier however,the two functions will combine and as in a conventional gas rectifierthe efiiciency of the device will decrease. Under normal operatingconditions the potential between the electrodes will not exceed theionization potential due to the fact that the main portion of thepotential applied to input transformer 34 will appear directly acrossthe load L.

Figure 5 shows a circuit diagram that is adapted for full Waverectification when utilizing the device shown in Figure 3. The circuitelements that are similar to those shown in Figure 4 will not bedescribed in detail. The main input transformer 34 is a conventionaltransformer with the secondary having a center tap to allow connectionto the filter circuit and the load. Since the operation of this circuitis similar to that of Figure 4, further discussion is not deemednecessary.

Figure 6 shows an embodiment of this invention which is used for thepurpose of half-wave rectification. The envelope 8 contains a main anodeI2 enclosing main cathode l4, auxiliary cathode l8 and auxiliary anode28. In this embodiment, as in the other embodiments, the par-' ticularelectrode arrangement is not critical. The operation of the main cathodeI4 and main anode l2 is similar to that described in connection withFigures 1 and 2 and will not be described in great detail in relation tothis figure. The plasma producing electrodes, i. e., the auxiliaryelectrodes, consist of auxiliary cathode l8 and auxiliary anode 28. Theauxiliary electrodes function as a conventional gas diode when connectedto an alternating current source.

In order to have a plasma within the device when the main circuitconducts some timing or phase shifting arrangements must be made betweenthe two circuits. With respect to time, as long as the auxiliaryelectrodes discharge be fore the main electrodes the device willfunction as desired. In other words the auxiliary electrodes dischargeand produce the conductive plasma a short time before the mainelectrodes conduct. The auxiliary electrodes may conduct for a longerperiod of time than the main electrodes. In the alternative, when theauxiliary electrodes and the main electrodes conduct for the same periodof time, the auxiliary electrodes conduct an instant before the mainelectrodes and thus form the plasma, the desired operation will takeplace. When this is done the plasma will not have suflicient time todiffuse out of the main path before the end of the conductive portion ofthe cycle in the main path.

Figure 7 is a circuit diagram that utilizes the device shown in Figure 6for the purpose of full wave rectification. In this figure the circuitelements are the same as described in connection with Figure 4 and sowillnot be described further. When desired some type of timing, or phaseshifting, device may be inserted in the main and/or auxiliary inputcircuits to insure that the various groups of electrodes will conduct atthe proper time.

I claim:

1. Rectifier apparatus comprising a gas discharge device, said gasdischarge device comprising an envelope containing an ionizable medium,a cathode and an anode in said envelope defining a main current path,means for forming and maintaining a plasma substantially throughout saidpath including at least one auxiliary thermionic cathode in saidenvelope and a source of alternating current potential, and saidauxiliary cathode being directly connected electrically solely to saidsource.

2. Rectifier apparatus operable when connected solely to a source of lowfrequency alternating current potential comprising a gas dischargedevice, said gas discharge device comprising an envelope containing anionizable medium, a cathode and an anode in said envelope defining amain current path, means for forming and maintaining a plasma along saidpath including at least one auxiliary thermionic cathode in saidenvelope and a source of alternating current potential, and saidauxiliary cathode being directly connected electrically solely to saidsource.

3. Rectifier apparatus comprising a gas discharge device, said gasdischarge device comprising an envelope having an ionizable mediumtherein, a thermionic cathode and an anode in said envelope defining amain current path, a source of low frequency alternating currentpotential, electrode means for forming and maintaining a plasmasubstantially throughout said path including at least one auxiliarythermionic cathode in said envelope, and said'auxiliary thermioniccathode being directly connected electrically solely to said source.

4. A gas discharge device, comprising a sealed envelope having anionizable medium therein, a hollow anode and a thermionic cathodedefining a main current path, means for forming and maintaining a plasmaalong said path including at least one auxiliary thermionic cathode,said anode surrounding said cathode and said means, all of saidelectrodes being adapted to be energized directly by an alternatingelectrical current.

5. A gas discharge device operable solely by an alternating electricalcurrent, comprising a sealed envelope having an ionizable mediumtherein, anode means and a thermionic cathode defining a main currentpath, electrode means for forming and maintaining a plasma along saidpath including at least one auxiliary thermionic cathode, and said anodemeans substantially surrounding said cathode and said electrode means.

6. A gas discharge device comprising a sealed envelope having anionizable medium therein, a hollow anode and a thermionic cathodedefining a main current path, a pair of auxiliary thermionic cathodesfor forming and maintaining a plasma along said path, said anodesurrounding all of said cathodes.

7. A gas discharge device comprising a sealed envelope having anionizable medium therein, a pair of elongated semi-circular shapedanodes and a thermionic cathode defining a pair of main current paths, apair of auxiliary cathodes for forming and maintaining a plasmasubstantially throughout both of said paths, and said anodessubstantially surrounding all of said cathodes.

8. A gas discharge device comprising a sealed envelope having anionizable medium therein, a hollow anode and a thermionic cathodedefining a main current path, an auxiliary thermionic cathode and anauxiliary anode for forming and maintaining a plasma along said pathduring the interval of time when said path is conducting, and said anodesurrounding all of said electrodes.

9. A gas discharge device comprising a sealed envelope having anionizable medium therein, a pair of elongated semi-circular shapedanodes and a thermionic cathode defining a pair of main current paths, apair of auxiliary thermionic cathodes for forming and maintaining aplasma substantially throughout said paths, said anode substantiallysurrounding all of said cathodes, insulating means between said pair ofanodes, said main cathode being coaxial with said anodes, said cathodesbeing aligned with the middle cathode being said main cathode, and saidauxiliary cathodes arranged on a line perpendicular to a line throughsaid insulating means and said main cathode.

10. A gas discharge device comprising a sealed envelope having anionizable medium therein, a tubular anode and a main thermionic cathodedefining a main current path, a pair of auxiliary thermionic cathodesfor forming and maintaining a plasma substantially throughout said path,said anode surrounding all of said cathodes, and insulating membersabutting the ends of said anode and said cathodes.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,863,702 Smith June 21, 1932 2,158,564 Meier May 16, 19392,409,717 Slack et al Oct. 22 1946 2,450,475 Hansell Oct. 5, 19482,578,571 Meier Dec. 11, 1951

